ArticleMetadataTest: Clear static cache during setup
ArticleMetadataTest: Clear static cache during setup

Without this, testValidatePageIds() breaks, because validatePageIds()
populates its cache while the test pages are being created but before
they are added to the queue.

Bug: T250643
Change-Id: I83843f7b488444c54cc56927ec0bc73ebed3a2be

wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage